CN111584842B - Preparation method of double-shell spherical lithium-rich layered oxide cathode material with crystal grain size arranged in direction - Google Patents

Preparation method of double-shell spherical lithium-rich layered oxide cathode material with crystal grain size arranged in direction Download PDF

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CN111584842B
CN111584842B CN202010424224.0A CN202010424224A CN111584842B CN 111584842 B CN111584842 B CN 111584842B CN 202010424224 A CN202010424224 A CN 202010424224A CN 111584842 B CN111584842 B CN 111584842B
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许保磊
李荐
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Hunan Zhengyuan Institute For Energy Storage Materials And Devices
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Abstract

The invention discloses a preparation method of a double-shell spherical lithium-rich layered oxide cathode material with crystal grain size arranged in the radial direction. The material has the advantages of simple preparation process, low production cost, environmental friendliness, hopeful realization of industrial mass production and wide application prospect.

Description

Preparation method of double-shell spherical lithium-rich layered oxide cathode material with crystal grain size arranged in direction
Technical Field
The invention belongs to the field of preparation of lithium ion battery electrode materials, and particularly relates to a preparation method of a double-shell spherical lithium-rich layered oxide anode material with crystal grain sizes distributed in a radial direction.
Background
At present, the energy density requirements of lithium ion batteries are continuously improved due to the rapid development in the fields of consumer electronics, electric automobiles and the like, and the traditional cathode materials can not meet the requirements gradually. The lithium-rich layered oxide has the general formula of xLi 2 MnO 3 •(1-x)LiMO 2 M = Ni or Co or Mn, mainly Li 2 MnO 3 And LiNi x1 Co x2 Mn x3 O 2 Two-component composition with structure similar to LiCoO 2 Having a high specific discharge capacity (>250 mAh/g), high output voltage, green safety, low production cost and the like, and is expected to become a candidate of a next-generation lithium ion battery cathode material.
However, the lithium-rich layered oxide positive electrode material has low first-turn coulombic efficiency, has the problem of voltage attenuation in the circulating process, and particularly has poor conductivity and insufficient high-rate charge and discharge capacity, so that the commercial application of the material is limited.
Disclosure of Invention
The invention aims to provide a preparation method of a double-shell spherical lithium-rich layered oxide cathode material with crystal grain diameter arranged in a radial direction. The general formula of the anode material is xLi 2 MnO 3 •(1-x)LiMO 2 And M = Ni or Co or Mn, the secondary particles are of a double-shell spherical structure, and crystal grains forming the secondary particles are radially grown and arranged in a divergent shape.
The invention is realized by the following technical scheme, which comprises the following specific steps:
(1) Preparation of solution A: respectively dissolving manganese salt, cobalt salt and nickel salt in water to obtain the solution A;
(2) Preparing a solution B: dissolving a precipitator and a complexing agent in water to obtain a solution B;
(3) Preparing a solution C: dissolving polyvinylpyrrolidone in water to obtain the solution C;
(4) Carrying out coprecipitation reaction in four stages: step one, dropwise adding the solution A in the step (1), the solution B in the step (2) and the solution C in the step (3) into a reactor to perform liquid-liquid coprecipitation reaction, wherein the reaction temperature is controlled to be 20-60 ℃, the pH value of the reaction solution is 6.0-9.0, the stirring speed is 300-3000 r/m, and the reaction time is 2-40 h; step two, stopping dripping the solution C, and performing other process conditions according to the step one; stage three, according to stage one; step four, according to the step two, finally obtaining a precipitate A;
(5) Cleaning the precipitate A obtained in the step (4) with deionized water, filtering and drying to obtain a precipitate B;
(6) Heating the precipitate B obtained in the step (5) to 300-600 ℃ at the heating rate of 1~5 ℃/min, and preserving the heat for 2-10 h to obtain an oxide precursor of the positive electrode material;
(7) And (4) uniformly mixing the oxide precursor obtained in the step (6) with lithium salt, placing the mixture in a calcining furnace, and sintering in an air atmosphere. The specific sintering process is as follows: 1. firstly heating to 500 ℃ at a heating rate of 1~5 ℃/min, and preserving heat for 2-10h; 2. heating to 600 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1-2h, and then cooling to 500 ℃ in an air cooling accelerating manner; 3. heating to 700 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1-2h, and then cooling to 500 ℃ in an air cooling and accelerating manner; 4. heating to 800 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1-2h, and then cooling to 500 ℃ in an air cooling accelerating manner; 5. heating to 800-1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 10-30h, and then cooling along with a furnace to obtain the double-shell spherical lithium-rich layered oxide cathode material with the radially arranged crystal grains.
In the preparation method, the manganese salt comprises manganese nitrate, manganese formate, manganese acetate, manganese chloride and manganese sulfate; the nickel salt comprises nickel nitrate, nickel formate, nickel acetate, nickel chloride and nickel sulfate; the cobalt salt comprises cobalt nitrate, cobalt formate, cobalt acetate, cobalt chloride and cobalt sulfate.
In the preparation method, the concentration of the metal cations in the solution A is 0.1-2.0 mol/L.
In the above preparation method, the precipitant comprises Na 2 CO 3 、NaHCO 3 、K 2 CO 3 、KHCO 3 。
In the preparation method, the complexing agent is one or more of ammonia water, ammonium bicarbonate and ammonium carbonate.
In the preparation method, the concentration of the precipitant in the solution B is 0.1-2.0 mol/L.
In the preparation method, the concentration of the complexing agent in the solution B is 0.01-1.0 mol/L.
In the preparation method, the concentration of the polyvinylpyrrolidone in the solution C is 0.1-5.0 g/L.
In the above preparation method, the lithium salt includes lithium hydroxide, lithium carbonate, lithium nitrate, lithium formate, and lithium acetate.
In the preparation method, the air cooling accelerated cooling means that the heating switch of the sintering furnace is closed and the circulating fan is started at the moment, and the circulating fan is closed and the heating switch is started after the temperature is reduced to the specified temperature; the speed of air cooling accelerated cooling is 2 to 20 ℃/second.
In fact, in the preparation process of the precursor, through carrying out coprecipitation reaction in four stages, the interval addition of the polypyrrolidone solution is controlled, so that the components of the polypyrrolidone are distributed in two layers in the spherical precursor particles. Therefore, in the later high-temperature sintering process of the precursor, the spherical particles are transited to the double-shell spherical particles due to the thermal decomposition and activity of the polyvinylpyrrolidone. Meanwhile, in the high-temperature sintering process of the material, a directional heat dissipation effect can be generated by adopting rapid cooling treatment or increasing the times of the rapid cooling treatment, so that the temperature gradient of material particles in the radial direction is increased, the material crystal grains are induced to grow along the radial direction, and the crystal axes of the crystal grains in the radial direction are longer and are orderly arranged. The combined action of the two components enables the lithium-rich layered oxide cathode material to have a double-shell spherical structure with radially arranged crystal grains.
The invention has the following beneficial effects:
(1) The anode material is of a double-shell spherical structure, so that full contact with electrolyte is ensured, the diffusion path of lithium ions is shortened, and the high-current charge and discharge capacity of the material is improved;
(2) The crystal grains in the material particles are radially arranged, the conductivity of the material is improved, and the lithium diffusion resistance in the material is reduced;
(3) The double-shell spherical lithium-rich layered oxide anode material with the crystal grain diameter arranged in the direction has better structural stability, and can effectively relieve stress damage caused by deformation in the lithium ion de-intercalation process.
Drawings
FIG. 1: SEM image of double-layer shell spherical lithium-rich layered oxide anode material with crystal grain diameter arranged in the radial direction.
FIG. 2: the SEM image of the internal structure of the double-shell spherical lithium-rich layered oxide cathode material with the grain diameter arranged in the radial direction is prepared.
FIG. 3: the XRD diffraction pattern of the double-layer shell spherical lithium-rich layered oxide cathode material with the grain diameter arranged in the radial direction is prepared.
FIG. 4: the C-V (specific capacity-voltage) curve of the double-layer shell spherical lithium-rich layered oxide anode material with the grain diameter arranged in the radial direction is prepared by the invention.
FIG. 5: the double-shell spherical lithium-rich layered oxide anode material with the crystal grain diameter arranged in the radial direction has specific discharge capacity under different multiplying powers.
Detailed Description
The technical solutions of the present invention are further described below with reference to the drawings, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Example 1
Preparing a solution A, weighing manganese sulfate, nickel sulfate and cobalt sulfate according to a molar ratio of Mn to Ni to Co = 4; preparing a solution B, weighing a certain amount of precipitator and complexing agent, and dissolving the precipitator and the complexing agent in deionized water, wherein the precipitator is sodium carbonate, the concentration of the sodium carbonate solution is 2mol/L, the complexing agent is ammonia water, and the concentration of the ammonia water is 0.1mol/L; dissolving polyvinylpyrrolidone in deionized water, stirring uniformly, and preparing 0.1g/L polyvinylpyrrolidone solution. Coprecipitation is carried out in four stages: step one, dropwise adding the solution A, the solution B and the polyvinylpyrrolidone solution into the deionized water solution, controlling the pH value of a reaction system to be 8.0, stirring at the speed of 800 rpm, controlling the solution temperature to be 50 ℃ and reacting for 12 hours; stopping dripping the polyvinylpyrrolidone solution, and keeping other conditions unchanged; stage three, the same as stage one; and the fourth stage is the same as the second stage. And after the reaction is finished, performing suction filtration, washing with deionized water, removing impurity ions, filtering, and performing vacuum drying treatment on the precipitate to obtain a carbonate product. Heating the obtained carbonate product to 500 ℃ at the heating rate of 5 ℃/min, and preserving the temperature for 5h to obtain an oxide precursor.
Uniformly mixing the obtained oxide precursor with lithium carbonate according to the stoichiometric ratio of 1.05 to the lithium-rich layered oxide, then placing the mixture in a high-temperature furnace, heating to 500 ℃ at the heating rate of 5 ℃/min, and keeping the temperature for 5h; continuously heating to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 2h, and then cooling to 500 ℃ at the cooling rate of 12 ℃/sec in an air cooling accelerating manner; continuously heating to 700 ℃ at the heating rate of 5 ℃/min, preserving heat for 2h, and then cooling to 500 ℃ at the cooling rate of 12 ℃/sec in an air cooling accelerating manner; continuously heating to 800 ℃ at the heating rate of 5 ℃/min, preserving the heat for 2h, and then cooling to 500 ℃ at the cooling rate of 12 ℃/sec in an air cooling accelerating manner; and then continuously heating to 900 ℃ at the heating rate of 5 ℃/min, preserving the heat for 20h, and then cooling along with the furnace to obtain the double-shell spherical lithium-rich layered oxide anode material with the crystal grains radially arranged. The scanning electron micrographs are shown in FIGS. 1 and 2.
FIG. 3 is XRD of double-shell spherical lithium-rich layered oxide anode material with radial-arranged crystal grainsAnd (6) pictures. The spectrum shows that the XRD curve has superlattice characteristic peaks. The composite material consists of two components, namely layered LiNi 1/3 Co 1/3 Mn 1/3 O 2 Phase and Li 2 MnO 3 Phase, liNi 1/3 Co 1/3 Mn 1/3 O 2 Belongs to a hexagonal R-3m space group, li 2 MnO 3 The phase belongs to a monoclinic system C2/m space group.
And (3) carrying out button cell preparation and test on the prepared lithium-rich layered oxide cathode material. And (3) carrying out charge-discharge test on the button cell at 2-4.8V at 0.1C, wherein the first circle of charge-discharge C-V curve is shown in figure 4, and the first circle of discharge specific capacity is 279.27 mAh/g. The button cell is subjected to rate performance test, the rate performance is shown in figure 5, and the discharge specific capacity of the button cell is about 279mAh/g, 261 mAh/g, 243 mAh/g, 226 mAh/g and 204 mAh/g respectively under 0.1C, 0.2C, 0.5C, 1C and 2C.
Example 2
Preparing a solution A, weighing manganese nitrate, nickel nitrate and cobalt nitrate according to a molar ratio of Mn to Ni to Co = 5; preparing a solution B, weighing a certain amount of a precipitator and a complexing agent, and dissolving the precipitator and the complexing agent in deionized water, wherein the precipitator is sodium bicarbonate, the concentration of the sodium bicarbonate solution is 0.1mol/L, the complexing agent is ammonium bicarbonate, and the concentration of the complexing agent is 0.01mol/L; dissolving polyvinylpyrrolidone in deionized water, stirring uniformly, and preparing 0.5g/L polyvinylpyrrolidone solution. Coprecipitation is carried out in four stages: step one, dropwise adding the solution A, the solution B and the polyvinylpyrrolidone solution into the deionized water solution, controlling the pH value of a reaction system to be 6.0, stirring at the speed of 300 revolutions per minute, reacting at the temperature of 20 ℃ for 40 hours; stopping dripping the polyvinylpyrrolidone solution, and keeping other conditions unchanged; stage three, the same as stage one; and the fourth stage is the same as the second stage. And after the reaction is finished, performing suction filtration, washing with deionized water, removing impurity ions, filtering, and performing vacuum drying treatment on the precipitate to obtain a carbonate product. Heating the obtained carbonate product to 300 ℃ at the heating rate of 1 ℃/min, and preserving the temperature for 2h to obtain an oxide precursor.
Uniformly mixing the obtained oxide precursor with lithium hydroxide according to the stoichiometric ratio of 1.05; continuously heating to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 1h, and then cooling to 500 ℃ at the cooling rate of 2 ℃/sec in an air cooling accelerating manner; continuously heating to 700 ℃ at the heating rate of 5 ℃/min, preserving heat for 1h, and then cooling to 500 ℃ at the cooling rate of 2 ℃/sec in an air cooling accelerating manner; continuously heating to 800 ℃ at the heating rate of 5 ℃/min, preserving heat for 1h, and then cooling to 500 ℃ at the cooling rate of 2 ℃/sec in an air cooling accelerating manner; and then continuously heating to 1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 10 hours, and then cooling along with the furnace to obtain the double-shell spherical lithium-rich layered oxide cathode material with the crystal grains radially arranged. The XRD diffraction pattern of the cathode material prepared in this example indicates that the synthesized material is lithium-rich layered oxide.
And (3) carrying out button cell preparation and test on the prepared lithium-rich layered oxide cathode material. And (3) carrying out charge-discharge test on the button cell at 2-4.8V at 0.1C, wherein the specific discharge capacity of the first ring is 283.19 mAh/g. The button cell is subjected to rate capability test, and the discharging specific capacities of the button cell are respectively about 283mAh/g, 262 mAh/g, 241 mAh/g, 220 mAh/g and 201 mAh/g under 0.1C, 0.2C, 0.5C, 1C and 2C.
Example 3
Preparing a solution A, weighing manganese formate, nickel formate and cobalt formate according to a molar ratio Mn: ni: co =4 = 1, and dissolving the manganese formate, nickel formate and cobalt formate in deionized water to prepare 1mol/L solution A; preparing a solution B, weighing a certain amount of precipitator and complexing agent, and dissolving in deionized water, wherein the precipitator is potassium carbonate, the concentration of the potassium carbonate solution is 1mol/L, the complexing agent is ammonium carbonate, and the concentration is 0.05mol/L; dissolving polyvinylpyrrolidone in deionized water, stirring uniformly, and preparing 5.0g/L polyvinylpyrrolidone solution. Coprecipitation is carried out in four stages: step one, dropwise adding the solution A, the solution B and the polyvinylpyrrolidone solution into the deionized water solution, controlling the pH value of a reaction system to be 9.0, stirring speed to be 3000 r/m, solution temperature to be 60 ℃ and reacting for 2 hours; stopping dripping the polyvinylpyrrolidone solution, and keeping other conditions unchanged; stage three, the same as stage one; and the fourth stage is the same as the second stage. And after the reaction is finished, performing suction filtration, washing with deionized water, removing impurity ions, filtering, and performing vacuum drying treatment on the precipitate to obtain a carbonate product. Heating the obtained carbonate product to 600 ℃ at the heating rate of 3 ℃/min, and preserving the temperature for 10h to obtain an oxide precursor.
Uniformly mixing the obtained oxide precursor and lithium nitrate according to the stoichiometric ratio of 1.05; continuously heating to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 1.5h, then cooling by air, and then cooling by air at the cooling rate of 20 ℃/sec to be accelerated to 500 ℃; continuously heating to 700 ℃ at the heating rate of 5 ℃/min, preserving heat for 1.5h, and then cooling to 500 ℃ at the cooling rate of 20 ℃/sec in an air cooling accelerating manner; continuously heating to 800 ℃ at the heating rate of 5 ℃/min, preserving heat for 1.5h, and then cooling to 500 ℃ at the cooling rate of 20 ℃/sec in an air cooling accelerating manner; and then continuously heating to 800 ℃ at the heating rate of 5 ℃/min, preserving the heat for 30h, and then cooling along with the furnace to obtain the double-shell spherical lithium-rich layered oxide cathode material with the crystal grains radially arranged. The XRD diffraction pattern of the cathode material prepared in this example indicates that the synthesized material is a lithium-rich layered oxide.
And (3) carrying out button cell preparation and test on the prepared lithium-rich layered oxide cathode material. And (3) carrying out charge-discharge test on the button cell at 2-4.8V at 0.1C, wherein the specific discharge capacity of the first ring is 278.26 mAh/g. The button cell is subjected to rate capability test, and the discharging specific capacities of the button cell are respectively about 278mAh/g, 259 mAh/g, 243 mAh/g, 222 mAh/g and 203 mAh/g under 0.1C, 0.2C, 0.5C, 1C and 2C.
Example 4
Preparing a solution A, weighing manganese acetate, nickel acetate and cobalt acetate according to a molar ratio of Mn to Ni to Co =4 = 1, and dissolving the manganese acetate, the nickel acetate and the cobalt acetate in deionized water to prepare 1mol/L solution A; preparing a solution B, weighing a certain amount of precipitator and complexing agent, and dissolving in deionized water, wherein the precipitator is potassium bicarbonate, the concentration of the potassium bicarbonate solution is 1mol/L, the complexing agent is 50% ammonia water and 50% ammonium bicarbonate, and the concentration of the mixed complexing agent is 0.05mol/L; dissolving polyvinylpyrrolidone in deionized water, stirring uniformly, and preparing 5.0g/L polyvinylpyrrolidone solution. Coprecipitation is carried out in four stages: step one, dropwise adding the solution A, the solution B and the polyvinylpyrrolidone solution into the deionized water solution, controlling the pH value of a reaction system to be 9.0, the stirring speed to be 3000 r/min, the solution temperature to be 60 ℃ and reacting for 10 hours; stopping dripping the polyvinylpyrrolidone solution, and keeping other conditions unchanged; stage three, the same stage one; and a fourth stage which is the same as the second stage. And after the reaction is finished, performing suction filtration, washing with deionized water, removing impurity ions, filtering, and performing vacuum drying treatment on the precipitate to obtain a carbonate product. Heating the obtained carbonate product to 600 ℃ at the heating rate of 3 ℃/min, and preserving the temperature for 10h to obtain an oxide precursor.
Uniformly mixing the obtained oxide precursor with lithium formate according to the stoichiometric ratio of 1.05; continuously heating to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 1.5h, and then cooling to 500 ℃ at the cooling rate of 10 ℃/sec in an air cooling accelerating manner; continuously heating to 700 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1.5h, and then cooling to 500 ℃ at the cooling rate of 10 ℃/sec in an air cooling and accelerating manner; continuously heating to 800 ℃ at the heating rate of 5 ℃/min, preserving heat for 1.5h, and then cooling to 500 ℃ at the cooling rate of 10 ℃/sec in an air cooling accelerating manner; and then continuously heating to 850 ℃ at the heating rate of 5 ℃/min, preserving the heat for 30 hours, and then cooling along with the furnace to obtain the double-shell spherical lithium-rich layered oxide anode material with the crystal grains radially arranged. The XRD diffraction pattern of the cathode material prepared in this example indicates that the synthesized material is lithium-rich layered oxide.
And (3) preparing and testing the prepared lithium-rich layered oxide cathode material for the button cell. And (3) carrying out charge-discharge test on the button cell at 2 to 4.8V at 0.1C, wherein the specific discharge capacity of a first ring is 277.09 mAh/g. The button cell is subjected to rate capability test, and the discharging specific capacities of the button cell are respectively 277mAh/g, 255 mAh/g, 246 mAh/g, 225 mAh/g and 206 mAh/g under 0.1C, 0.2C, 0.5C, 1C and 2C.
Example 5
Preparing a solution A, weighing manganese chloride, nickel chloride and cobalt chloride according to a molar ratio of Mn to Ni to Co =4 = 1, and dissolving the manganese chloride, the nickel chloride and the cobalt chloride in deionized water to prepare 1mol/L solution A; preparing a solution B, weighing a certain amount of precipitator and complexing agent, and dissolving in deionized water, wherein the precipitator is potassium carbonate, the concentration of the potassium carbonate solution is 1mol/L, the complexing agent is ammonia water, and the concentration is 0.05mol/L; dissolving polyvinylpyrrolidone in deionized water, stirring uniformly, and preparing 5.0g/L polyvinylpyrrolidone solution. Coprecipitation is carried out in four stages: step one, dropwise adding the solution A, the solution B and the polyvinylpyrrolidone solution into the deionized water solution, controlling the pH value of a reaction system to be 8.2, the stirring speed to be 2000 rpm, the solution temperature to be 55 ℃, and reacting for 15 hours; stopping dripping the polyvinylpyrrolidone solution, and keeping other conditions unchanged; stage three, the same as stage one; and the fourth stage is the same as the second stage. And after the reaction is finished, performing suction filtration, washing with deionized water, removing impurity ions, filtering, and performing vacuum drying treatment on the precipitate to obtain a carbonate product. Heating the obtained carbonate product to 500 ℃ at a heating rate of 3 ℃/min, and preserving the temperature for 10h to obtain an oxide precursor.
Uniformly mixing the obtained oxide precursor with lithium acetate according to the stoichiometric ratio of 1.05; continuously heating to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 2h, and then cooling to 500 ℃ at the cooling rate of 12 ℃/sec in an air cooling accelerating manner; continuously heating to 700 ℃ at the heating rate of 5 ℃/min, preserving heat for 2h, and then cooling to 500 ℃ at the cooling rate of 12 ℃/sec in an air cooling accelerating manner; continuously heating to 800 ℃ at the heating rate of 5 ℃/min, preserving heat for 2h, and then cooling to 500 ℃ at the cooling rate of 12 ℃/sec in an air cooling accelerating manner; and then continuously heating to 900 ℃ at the heating rate of 5 ℃/min, preserving the heat for 24h, and then cooling along with the furnace to obtain the double-shell spherical lithium-rich layered oxide anode material with the crystal grains radially arranged. The XRD diffraction pattern of the cathode material prepared in this example indicates that the synthesized material is lithium-rich layered oxide.
And (3) carrying out button cell preparation and test on the prepared lithium-rich layered oxide cathode material. And (3) carrying out charge-discharge test on the button cell at 2-4.8V at 0.1C, wherein the specific discharge capacity of the first ring is 275.61 mAh/g. The button cell is subjected to rate capability test, and the discharging specific capacities of the button cell are respectively about 275mAh/g, 259 mAh/g, 244 mAh/g, 221 mAh/g and 206 mAh/g under 0.1C, 0.2C, 0.5C, 1C and 2C.

Claims (9)

1. A preparation method of a double-shell spherical lithium-rich layered oxide cathode material with crystal grain diameter arranged in a direction is characterized by comprising the following steps: the general formula of the cathode material is xLi 2 MnO 3 •(1-x)LiMO 2 M is the combination of three elements of Ni, co and Mn, and the preparation method comprises the following steps:
(1) Preparation of solution A: respectively dissolving manganese salt, cobalt salt and nickel salt in water to obtain the solution A;
(2) Preparing a solution B: dissolving a precipitator and a complexing agent in water to obtain a solution B;
(3) Preparation of solution C: dissolving polyvinylpyrrolidone in water to obtain the solution C;
(4) Carrying out coprecipitation reaction in four stages: step one, dropwise adding the solution A in the step (1), the solution B in the step (2) and the solution C in the step (3) into a reactor to perform liquid-liquid coprecipitation reaction, wherein the reaction temperature is controlled to be 20-60 ℃, the pH value of the reaction solution is 6.0-9.0, the stirring speed is 300-3000 r/m, and the reaction time is 2-40 h; step two, stopping dripping the solution C, and performing other process conditions according to the step one; stage three, according to stage one; step four, according to the step two, finally obtaining a precipitate A;
(5) Cleaning the precipitate A obtained in the step (4) with deionized water, filtering and drying to obtain a precipitate B;
(6) Heating the precipitate B obtained in the step (5) to 300-600 ℃ at a heating rate of 1~5 ℃/min, and preserving heat for 2-10h to obtain an oxide precursor of the positive electrode material;
(7) Uniformly mixing the oxide precursor obtained in the step (6) with lithium salt, placing the mixture in a calcining furnace, and sintering in an air atmosphere; the specific sintering process is as follows: 1. firstly heating to 500 ℃ at a heating rate of 1~5 ℃/min, and preserving heat for 2-10h; 2. heating to 600 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1-2h, and then cooling to 500 ℃ in an air cooling accelerating manner; 3. heating to 700 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1-2h, and then cooling to 500 ℃ in an air cooling and accelerating manner; 4. heating to 800 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1-2h, and then cooling to 500 ℃ in an air cooling accelerating manner; 5. heating to 800-1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 10-30h, and then cooling along with a furnace to obtain the double-shell spherical lithium-rich layered oxide cathode material with the radially arranged crystal grains.
2. The method for preparing the double-shell spherical lithium-rich layered oxide cathode material with the crystal grain size arranged in the radial direction according to claim 1, is characterized in that: in the step (1), the manganese salt comprises manganese nitrate, manganese formate, manganese acetate, manganese chloride and manganese sulfate; the nickel salt comprises nickel nitrate, nickel formate, nickel acetate, nickel chloride and nickel sulfate; the cobalt salt comprises cobalt nitrate, cobalt formate, cobalt acetate, cobalt chloride and cobalt sulfate.
3. The method for preparing the double-shell spherical lithium-rich layered oxide cathode material with the crystal grain size arranged in the radial direction according to claim 1, is characterized in that: in the solution A in the step (1), the concentration of metal cations is 0.1-2.0 mol/L.
4. The preparation method of the double-shell spherical lithium-rich layered oxide cathode material with the grain size arranged in the radial direction according to claim 1, is characterized in that: in step (2), the precipitating agent comprises Na 2 CO 3 、NaHCO 3 、K 2 CO 3 、KHCO 3 。
5. The preparation method of the double-shell spherical lithium-rich layered oxide cathode material with the grain size arranged in the radial direction according to claim 1, is characterized in that: in the step (2), the complexing agent is one or more of ammonia water, ammonium bicarbonate and ammonium carbonate.
6. The method for preparing the double-shell spherical lithium-rich layered oxide cathode material with the crystal grain size arranged in the radial direction according to claim 1, is characterized in that: in the step (2), the concentration of the precipitant in the solution B is 0.1-2.0 mol/L.
7. The method for preparing the double-shell spherical lithium-rich layered oxide cathode material with the crystal grain size arranged in the radial direction according to claim 1, is characterized in that: in the step (2), the concentration of the complexing agent in the solution B is 0.01-1.0 mol/L.
8. The method for preparing the double-shell spherical lithium-rich layered oxide cathode material with the crystal grain size arranged in the radial direction according to claim 1, is characterized in that: and (4) in the solution C in the step (3), the concentration of polyvinylpyrrolidone is 0.1-5.0 g/L.
9. The preparation method of the double-shell spherical lithium-rich layered oxide cathode material with the grain size arranged in the radial direction according to claim 1, is characterized in that: in the step (7), the lithium salt includes lithium carbonate, lithium nitrate, lithium formate, and lithium acetate.
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